gatk: correct license and add zlib-ng-compat on Linux

[BenjaminDEMAILLE]

LICENSE.TXT in the GATK repository is the Apache License 2.0, not BSD-3-Clause:

   Copyright 2021 Broad Institute, Inc.

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this software except in compliance with the License.

Same text on the 4.6.2.0 tag currently packaged here and on the latest 4.7.0.0; the file contains no BSD terms. GitHub's licence API reports NOASSERTION because of the copyright header above the standard text, which is likely where the original value came from.

Metadata only, no revision bump.

AI-assisted contribution by Claude Code (Claude Opus 5). The licence text was checked against both tags and brew style was run; I reviewed the change before opening this PR and will answer review comments myself.

[YoshitakaMo]

Please include depends_on "zlib-ng-compat" for Linux build to fix the error: https://github.com/brewsci/homebrew-bio/actions/runs/32569830013 .